1. Field of the Invention
This invention relates generally to aircraft lavatory waste handling systems and more particularly to an improved drain valve for sealing an aircraft waste disposal drain line.
2. Prior Art
Commercial passenger airliners and other commercial aircraft have lavatories whose waste is collected, during flight, in one or more tanks on board the aircraft. These tanks are drained at airport facilities through drain lines on the aircraft having outlet ends which are located at waste disposal service panels on the exterior of the aircraft for connection to an airport waste disposal system. The outlet end of each drain line is normally closed by a sealing device or valve which is accessible at the respective service panel for operation between open and closed positions by aircraft servicing personnel. Also located at the service panels are handles for operating collecting tank drain valve(s) on the aircraft, and flush/fill ports for flushing and replenishing the collecting tank(s) after they have been drained.
One type of existing drain line sealing device is a bi-conduit valve including a body having an inlet for connection to the outlet end of an aircraft drain line, an outlet for connection to an airport drain hose, and a doughnut plug within the valve body which is extendable and retractable into and from a drain passage extending between the inlet and outlet. This plug, when extended into the drain passage, is expandable radially into fluid sealing and interlocking engagement with the wall of the passage in such a way as to seal the passage and lock the plug in sealing position. U.S. Pat. Nos. 3,954,123 and 4,027,701 disclose aircraft drain line sealing devices of this kind.
U.S. Pat. No. 4,098,427 discloses another type of existing aircraft drain line sealing device. This sealing device is a cap having an inlet for connection to the outlet end of an aircraft drain line, an outlet for connection to an airport drain hose, and two seals arranged in series along a waste passage extending between the inlet and outlet. One seal is a hinged outer valve cover which is pivotally movable between a closed position against a valve seat about the cap outlet and an open position spaced from the seat in which the cap outlet is accessible for connection to an airport drain hose. The other seal of the cap is an inner valve flapper pivotally mounted within the cap passage for swinging between a closed position against a valve seat about the passage and an open position spaced from the seat.
An aircraft waste collecting tank is emptied at an airport facility by connecting the outlet of the corresponding aircraft drain line sealing device to a drain hose at the facility and then opening the drain passage through the sealing device by retracting its sealing plug or opening its inner valve flapper, as the case may be, to permit the contents of the aircraft collecting tank to drain into the airport waste receiver. The empty aircraft collecting tank is then flushed and recharged, the airport drain hose is removed, and the aircraft drain line sealing device is reclosed.
The existing aircraft drain line sealing devices of this kind have many deficiencies. Perhaps the most serious of these is their tendency to leak toilet fluids. These toilet fluids are corrosive to aircraft structures and can also create a serious problem involving so-called "blue ice". The existing sealing devices are prone to leaking for the reasons explained below. Suffice it to say at this point that the very low ambient temperatures at normal aircraft cruising altitudes cause the leakage fluids to freeze almost instantaneously into what is commonly called "blue ice". This leakage of waste fluids, if it occurs, generally continues throughout most of the flight and results in the formation of a very sizeable blue ice mass which can, and often does, separate from the aircraft. Such a separated blue ice mass can cause serious damage to the aircraft structure or engines or fall to the ground and cause serious damage to buildings and injury to persons on the ground. Separation of blue ice from an aircraft is particularly prone to occur during descent of an aircraft from its cruising altitude due to the increase in ambient temperature which occurs with decreasing altitude.
A number of such blue ice separation incidents have occured in the past with very serious and potentially fatal consequences. In one such incident, for example, the separated blue ice mass was ingested into and caused abrupt stoppage of an engine. This abrupt stoppage of the engine, in turn, produced intense torsional stresses which caused complete separation of the engine from the aircraft. In another incident, the separated blue ice mass fell through and caused severe damage to a house. It is only a matter of time until such a blue ice separation incident causes death by striking a person on the ground or by loss of an entire aircraft.
The existing aircraft drain line sealing devices have certain characteristics construction and operation which either render these devices prone to the leakage problem just discussed or exacerbate the problem. For example, both the existing drain line sealing cap and plug devices have sealing surfaces which are exposed to direct impact by the waste being drained. These sealing surfaces are the surface of a seal ring on the inner valve flapper of the drain line sealing cap and the sealing surface which is engaged by the plug of the plug-type sealing device. The waste drained from an aircraft often contains sharp or hard objects, such as razor blades, hair pins, and the like, which can cut, score, or otherwise damage such sealing surfaces sufficiently to cause waste leakage in flight.
Another deficiency of the existing aircraft drain line sealing devices having inner hinged valve flappers resides in the fact that these flappers often do not seal properly due to the presence of a waste obstruction between the flappers and their valve seats. Thus, a hinged valve flapper opens and closes laterally of its valve seat, so that any obstruction remaining between the flapper and the seat when closing the flapper will prevent proper seating of the flapper and cause waste leakage. The inner valve flapper is particularly vulnerable to such improper seating since neither its upstream seating side nor its valve seat can be easily viewed to determine if any waste is adhering to the flapper or seat which might obstruct proper seating of the flapper. As a consequence, if the inner flapper is closed blindly without careful inspection of its seating side and its valve seat by the waste disposal crew, the flapper may not seat properly when closed. Such improper seating of the inner flapper is not readily evident in most cases until the valve leaks during the next flight with the resultant formation of blue ice or blue streaks on the aircraft skin or waste discharge occurs when the outer valve cover is opened during the next ground servicing of the waste disposal system, as discussed below. The existing plug-type drain line sealing devices are similarly deficient to a certain degree in that their interior sealing surfaces which are engaged by the doughnut plug are difficult to inspect for adhering waste material which might obstruct proper sealing of the waste passage through the cap by the plug.
The inner and outer seals, i.e. the inner doughnut plug or valve flapper and the outer valve cover, of the existing drain line sealing devices are intended to provide sealing redundancy. Leakage of the inner doughnut plug or valve flapper in flight has very undesirable consequences, however, even though the outer valve cover seals properly and thus prevents the formation of blue ice on the exterior of the aircraft. These undesirable consequences involve sudden discharge of the leaked waste onto the ground, onto equipment, and/or onto the waste disposal personnel when the outer cover is opened during the next servicing of the aircraft at an airline facility. This waste discharge is commonly referred to as a "dump", particularly if it is relatively sizeable as discussed below.
The existing drain line caps or valves of the kind disclosed in U.S. Pat. No. 4,098,427 are particularly prone to such "dumps". This is due to the fact that outer cover of these valves are designed to close the inner valve flapper when the cover is closed, and the valves have a latch which is intended to automatically lock the inner valve flapper closed upon its movement to its closed position by the cover. For this reason, waste disposal personnel are generally required to close the drain valve in only one step by closing the outer cover with the assumption that the inner valve flapper will thereby be latched closed. Due to the buildup of manufacturing tolerances, wear, and other factors, however, closure of the cover often does not result in latching of the inner flapper. In this case, not only does waste leak freely past the inner flapper in flight, but opening of the outer cover on the ground permits the inner flapper to immediately open wide by the pressure of the waste behind the flapper and thus dump a sizeable quantity of waste. While this dump can be avoided by closing the valve in two steps by first closing the inner flapper and making sure it latches and then closing the outer cover, waste disposal personnel are not required to and thus generally do not follow this two step procedure.
Another deficiency of the existing drain line sealing devices resides in the fact that they are very difficult to open when frozen. Thus, because of the very low ambient temperatures at normal aircraft cruising altitudes, the waste within and condensation on the exterior of the sealing devices freezes. As a consequence, it is very difficult, if not impossible, to open their hinged valve flappers or remove their sealing plugs immediately after landing without prying the flappers or plugs loose. For this reason, airline waste disposal personnel often attempt to use implements of one kind or another to loosen or pry open a frozen drain line valve or remove a frozen drain line plug. This often damages their sealing surfaces and results in valve or plug leakage in flight.
Even if a frozen plug can be removed or a frozen valve flapper can be opened, the waste behind the plug or inner valve flapper is generally frozen and blocks draining of waste from the aircraft. The existing drain line sealing devices do not permit such a frozen waste blockage to be eliminated in any satisfactory way. For example, about the only way of eliminating such a frozen waste blockage is to use a pick to chip away the frozen mass of waste through the open drain passage which exists after removal of the sealing plug or opening of the inner valve flapper. Since the drain passage is then wide open, however, sudden release or breakup of the frozen waste mass will, and often does, result in a large waste dump. For these reasons, when frozen conditions such as those discussed above exist, airline waste disposal personnel may simply not drain aircraft waste collection tanks, and thereby creates the possibility of even a more serious waste dump during the next aircraft servicing.
The inner valve flappers of many aircraft drain line sealing devices are very difficult to both open and close, whether frozen or not, because of their hinged construction and their use of diametral seal rings, that is, seal rings which seat radially outward against a surrounding cylindrical sealing surface. Thus, a hinged flapper is essentially a cantilever-like arm which is hinged at one end and rotated by a torque applied on its hinge axis to swing its free end laterally toward and away from the flapper valve seat. Forces acting on this free end of the flapper resist pivoting of the flapper with a substantial mechanical advantage. The frozen waste referred to above exerts such resisting forces on the inner flapper. Sliding engagement and disengagement of diametral flapper seal rings also produce substantial frictional resisting forces on the flappers which render opening and closing of the flapper very difficult without lubrication. Such seal ring lubrication is not permitted on aircraft drain line valves, however. The doughnut plugs which are used in some drain line sealing devices are also difficult to remove the reasons mentioned above. Another disadvantage of such plugs resides in the fact that they are radially expanded and contracted by a removable wrench. Quite often when removing or installing such a plug, it will accidently separate from its wrench and will be damaged or lost.
The existing drain line valves having inner hinged flappers have springs which are intended to open the flappers when the flapper latches are released. Quite frequently, these springs are ineffective, however, because they are not strong enough to overcome the above resisting forces exerted on the flappers by ice and diametral seating flapper seal rings.
The above disadvantages of inner valve flappers and doughnut plugs are exacerbated by the material from which the flapper seal rings and the sealing portion of the plugs are fabricated. This material is an elastomer material which tends to swell when contacted by toilet fluids and to harden with age. Both of these characteristics increase the resistance imposed on a flapper during its opening and closing movement and on a plug during its removal and installation. The seal rings of the existing drain line valves are also commonly contained within grooves or the like and retained in the grooves only by friction, rather than by positive retention means. As a consequence, the seal rings frequently drop out of their grooves, particularly after they have swelled and/or hardened somewhat by age, and are either lost or damaged.
The outer cover seals of many existing drain line sealing devices include face-type valve seats about the hose couplings of the devices which are engaged by seal rings on the covers when the covers are closed. These face seats are exposed to potentially damaging contact by the couplings of airline waste disposal hoses when the hoses are connected to or removed from the devices. The prior sealing devices are also have a large number of intricate parts which are difficult to fabricate and assemble so that the prior devices tend to be costly to manufacture and maintain in proper working condition.
Finally, as discussed later, the Federal Aviation Admistration has recently issued a new regulation which requires periodic leak testing of aircraft drain valves and flush/fill ports. Because of the design of the existing aircraft drain line sealing devices, the new regulation presents certain problems in connection with the leak testing of such sealing devices.
It is evident at this point, therefore, that there is a definite need for an improved aircraft drain line sealing device.